Adsorptive materials or adsorbents are solids which are able to adsorb considerable amount of gas or liquid, and are widely used in various industrial applications, such as water purifications, bleaching and purifying of fats and oils, drying of air, etc. Being one of the most important adsorbents, synthetic magnesium silicate has gained much attention in the last two decades for regeneration of used frying oil and purification of biodiesel in addition to having been used for column chromatography. Florisil®, Magnesol XL®, and Mizukaife F1® can be counted as being some of the commercially available synthetic magnesium silicates.
Synthetic magnesium silicate (MgO.nSiO2.xH2O) is produced by mixing solutions of sodium silicate and magnesium salts. Sodium silicate is usually prepared by smelting of quartz sand and sodium carbonate at about 1400° C. temperature in ordinary glass-melting furnace. Instead of this high temperature process, a simple low energy chemical method has been proposed to extract amorphous silica from rice hull ash, a co-product of rice industry (Kamath and Proctor, 1998).
Rice hulls or rice husk, a waste co-product of rice industry, contains over 60% silica and are evaluated as raw material for production of a number of silica based products.
When harvested from field, rice kernels are fully enveloped by rice hulls. After being harvested, first stage in milling is removal of hulls. Rice hulls comprise 20-25% of kernel, and mainly contain lignin, cellulose, hemicellulose and silica. Rice hulls are combusted to produce rice hull ash that contains more than 60% silica. Rice hull and rice hull ash have become a source for a number of silicon compounds, including silicon carbide, silicone nitrit, silicone tetrachloride, zeolite, pure silicon, silica, silica gel, sodium silicate.